Chapter 6: A Tour of the Cell PDF

LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 6 A Tour of the Cell Click t...

LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 6 A Tour of the Cell Click to add text Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Overview: The Fundamental Units of Life All organisms are made of cells The cell is the simplest collection of matter that can be alive Cell structure is correlated to cellular function All cells are related by their descent from earlier cells © 2011 Pearson Education, Inc. Figure 6.1 Concept 6.1: Biologists use microscopes and the tools of biochemistry to study cells Though usually too small to be seen by the unaided eye, cells can be complex © 2011 Pearson Education, Inc. Microscopy Scientists use microscopes to visualize cells too small to see with the naked eye In a light microscope (LM), visible light is passed through a specimen and then through glass lenses Lenses refract (bend) the light, so that the image is magnified © 2011 Pearson Education, Inc.  Three important parameters of microscopy – Magnification, the ratio of an object’s image size to its real size – Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points – Contrast, visible differences in parts of the sample © 2011 Pearson Education, Inc. Figure 6.2 10 m Human height 1m Length of some nerve and Unaided eye muscle cells 0.1 m Chicken egg 1 cm Frog egg 1 mm Light microscopy Human egg 100 m Most plant and animal cells 10 m Nucleus Most bacteria Electron microscopy Mitochondrion 1 m Smallest bacteria Super- 100 nm Viruses resolution microscopy Ribosomes 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms Figure 6.2a 10 m Human height 1m Length of some nerve and Unaided eye muscle cells 0.1 m Chicken egg 1 cm Frog egg 1 mm Human egg 100 m Figure 6.2b 1 cm Frog egg 1 mm Light microscopy Human egg 100 m Most plant and animal cells 10 m Nucleus Most bacteria Electron microscopy Mitochondrion 1 m Smallest bacteria Super- 100 nm Viruses resolution microscopy Ribosomes 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms Figure 6.3 Light Microscopy (LM) Electron Microscopy (EM) Brightfield Confocal Longitudinal section Cross section (unstained specimen) of cilium of cilium Cilia 50 m Brightfield (stained specimen) 50 m 2 m 2 m Transmission electron Scanning electron microscopy (TEM) Deconvolution microscopy (SEM) Phase-contrast 10 m Differential-interference- contrast (Nomarski) Super-resolution Fluorescence 1 m 10 m Figure 6.3a Brightfield (unstained specimen) 50 m Figure 6.3b Brightfield (stained specimen) Figure 6.3c Phase-contrast Figure 6.3d Differential-interference- contrast (Nomarski) Figure 6.3e Fluorescence 10 m Figure 6.3f Confocal 50 m Figure 6.3fa Confocal 50 m Figure 6.3fb Confocal 50 m Figure 6.3g Deconvolution 10 m Figure 6.3h Super-resolution 1 m Figure 6.3ha Super-resolution 1 m Figure 6.3hb Super-resolution 1 m Figure 6.3i Cilia 2 m Scanning electron microscopy (SEM) Figure 6.3j Longitudinal section Cross section of cilium of cilium 2 m Transmission electron microscopy (TEM)  LMs can magnify effectively to about 1,000 times the size of the actual specimen Various techniques enhance contrast and enable cell components to be stained or labeled Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by an LM © 2011 Pearson Education, Inc.  Two basic types of electron microscopes (EMs) are used to study subcellular structures Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen TEMs are used mainly to study the internal structure of cells © 2011 Pearson Education, Inc.  Recent advances in light microscopy – Confocal microscopy and deconvolution microscopy provide sharper images of three- dimensional tissues and cells – New techniques for labeling cells improve resolution © 2011 Pearson Education, Inc. Cell Fractionation Cell fractionation takes cells apart and separates the major organelles from one another Centrifuges fractionate cells into their component parts Cell fractionation enables scientists to determine the functions of organelles Biochemistry and cytology help correlate cell function with structure © 2011 Pearson Education, Inc. Figure 6.4 TECHNIQUE Homogenization Tissue cells Homogenate Centrifuged at 1,000 g (1,000 times the Centrifugation force of gravity) for 10 min Supernatant poured into next tube Differential centrifugation 20,000 g 20 min 80,000 g 60 min Pellet rich in nuclei and cellular debris 150,000 g 3 hr Pellet rich in mitochondria (and chloro- plasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal membranes) Pellet rich in ribosomes Figure 6.4a TECHNIQUE Homogenization Tissue cells Homogenate Centrifugation Figure 6.4b TECHNIQUE (cont.) Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min Supernatant poured into next tube Differential centrifugation 20,000 g 20 min 80,000 g 60 min Pellet rich in nuclei and cellular debris 150,000 g 3 hr Pellet rich in mitochondria (and chloro- plasts if cells are from a plant) Pellet rich in “microsomes” Pellet rich in ribosomes Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells Protists, fungi, animals, and plants all consist of eukaryotic cells © 2011 Pearson Education, Inc. Comparing Prokaryotic and Eukaryotic Cells Basic features of all cells – Plasma membrane – Semifluid substance called cytosol – Chromosomes (carry genes) – Ribosomes (make proteins) © 2011 Pearson Education, Inc.  Prokaryotic cells are characterized by having – No nucleus – DNA in an unbound region called the nucleoid – No membrane-bound organelles – Cytoplasm bound by the plasma membrane © 2011 Pearson Education, Inc. Figure 6.5 Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 m (a) A typical Flagella (b) A thin section rod-shaped through the bacterium bacterium Bacillus coagulans (TEM) Figure 6.5a 0.5 m (b) A thin section through the bacterium Bacillus coagulans (TEM)  Eukaryotic cells are characterized by having – DNA in a nucleus that is bounded by a membranous nuclear envelope – Membrane-bound organelles – Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally much larger than prokaryotic cells © 2011 Pearson Education, Inc.  The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell The general structure of a biological membrane is a double layer of phospholipids © 2011 Pearson Education, Inc. Figure 6.6 (a) TEM of a plasma Outside of cell membrane Inside of cell 0.1 m Carbohydrate side chains Hydrophilic region Hydrophobic region Hydrophilic Phospholipid Proteins region (b) Structure of the plasma membrane Figure 6.6a Outside of cell Inside of cell 0.1 m (a) TEM of a plasma membrane  Metabolic requirements set upper limits on the size of cells The surface area to volume ratio of a cell is critical As the surface area increases by a factor of n2, the volume increases by a factor of n3 Small cells have a greater surface area relative to volume © 2011 Pearson Education, Inc. Figure 6.7 Surface area increases while total volume remains constant 5 1 1 Total surface area [sum of the surface areas (height  width) of all box 6 150 750 sides  number of boxes] Total volume [height  width  length  number of boxes] 1 125 125 Surface-to-volume (S-to-V) ratio [surface area  volume] 6 1.2 6 A Panoramic View of the Eukaryotic Cell A eukaryotic cell has internal membranes that partition the cell into organelles Plant and animal cells have most of the same organelles © 2011 Pearson Education, Inc.  BioFlix: Tour of an Animal Cell © 2011 Pearson Education, Inc.  BioFlix: Tour of a Plant Cell © 2011 Pearson Education, Inc. Figure 6.8a ENDOPLASMIC RETICULUM (ER) Nuclear Rough Smooth envelope Flagellum ER ER NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome Figure 6.8b Animal Cells Fungal Cells 1 m 10  m Parent cell Cell wall Buds Vacuole Cell 5 m Nucleus Nucleus Nucleolus Mitochondrion Human cells from lining Yeast cells budding A single yeast cell of uterus (colorized TEM) (colorized SEM) (colorized TEM) Figure 6.8ba Animal Cells 10 m Cell Nucleus Nucleolus Human cells from lining of uterus (colorized TEM) Figure 6.8bb Fungal Cells Parent cell Buds 5 m Yeast cells budding (colorized SEM) Figure 6.8bc 1 m Cell wall Vacuole Nucleus Mitochondrion A single yeast cell (colorized TEM) Figure 6.8c Nuclear Rough envelope endoplasmic NUCLEUS reticulum Smooth Nucleolus endoplasmic reticulum Chromatin Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate CYTOSKELETON filaments Microtubules Mitochondrion Peroxisome Plasma membrane Chloroplast Cell wall Plasmodesmata Wall of adjacent cell Figure 6.8d Plant Cells Protistan Cells Flagella 1 m Cell 5 m 8 m Cell wall Nucleus Chloroplast Nucleolus Mitochondrion Vacuole Nucleus Nucleolus Chloroplast Chlamydomonas Cells from duckweed (colorized SEM) Cell wall (colorized TEM) Chlamydomonas (colorized TEM) Figure 6.8da Plant Cells Cell 5 m Cell wall Chloroplast Mitochondrion Nucleus Nucleolus Cells from duckweed (colorized TEM) Figure 6.8db Protistan Cells 8 m Chlamydomonas (colorized SEM) Figure 6.8dc Protistan Cells 1 m Flagella Nucleus Nucleolus Vacuole Chloroplast Cell wall Chlamydomonas (colorized TEM) Concept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes The nucleus contains most of the DNA in a eukaryotic cell Ribosomes use the information from the DNA to make proteins © 2011 Pearson Education, Inc. The Nucleus: Information Central The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle The nuclear envelope encloses the nucleus, separating it from the cytoplasm The nuclear membrane is a double membrane; each membrane consists of a lipid bilayer © 2011 Pearson Education, Inc. Figure 6.9 1 m Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Pore complex Surface of nuclear envelope Ribosome Close-up 0.25 m of nuclear Chromatin envelope 1 m Pore complexes (TEM) Nuclear lamina (TEM) Figure 6.9a Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Pore complex Ribosome Close-up of nuclear Chromatin envelope Figure 6.9b 1 m Nuclear envelope: Inner membrane Outer membrane Nuclear pore Surface of nuclear envelope Figure 6.9c 0.25 m Pore complexes (TEM) Figure 6.9d 1 m Nuclear lamina (TEM)  Pores regulate the entry and exit of molecules from the nucleus The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein © 2011 Pearson Education, Inc.  In the nucleus, DNA is organized into discrete units called chromosomes Each chromosome is composed of a single DNA molecule associated with proteins The DNA and proteins of chromosomes are together called chromatin Chromatin condenses to form discrete chromosomes as a cell prepares to divide The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis © 2011 Pearson Education, Inc. Ribosomes: Protein Factories Ribosomes are particles made of ribosomal RNA and protein Ribosomes carry out protein synthesis in two locations – In the cytosol (free ribosomes) – On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes) © 2011 Pearson Education, Inc. Figure 6.10 0.25 m Free ribosomes in cytosol Endoplasmic reticulum (ER) Ribosomes bound to ER Large subunit Small subunit TEM showing ER and ribosomes Diagram of a ribosome Figure 6.10a 0.25 m Free ribosomes in cytosol Endoplasmic reticulum (ER) Ribosomes bound to ER TEM showing ER and ribosomes Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell Components of the endomembrane system – Nuclear envelope – Endoplasmic reticulum – Golgi apparatus – Lysosomes – Vacuoles – Plasma membrane These components are either continuous or connected via transfer by vesicles © 2011 Pearson Education, Inc. The Endoplasmic Reticulum: Biosynthetic Factory The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells The ER membrane is continuous with the nuclear envelope There are two distinct regions of ER – Smooth ER, which lacks ribosomes – Rough ER, surface is studded with ribosomes © 2011 Pearson Education, Inc. Figure 6.11 Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Transitional ER Ribosomes Transport vesicle 200 nm Smooth ER Rough ER Figure 6.11a Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Transitional ER Ribosomes Transport vesicle Figure 6.11b Smooth ER Rough ER 200 nm Functions of Smooth ER The smooth ER – Synthesizes lipids – Metabolizes carbohydrates – Detoxifies drugs and poisons – Stores calcium ions © 2011 Pearson Education, Inc. Functions of Rough ER The rough ER – Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates) – Distributes transport vesicles, proteins surrounded by membranes – Is a membrane factory for the cell © 2011 Pearson Education, Inc. The Golgi Apparatus: Shipping and Receiving Center The Golgi apparatus consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus – Modifies products of the ER – Manufactures certain macromolecules – Sorts and packages materials into transport vesicles © 2011 Pearson Education, Inc. Figure 6.12 cis face (“receiving” side of 0.1 m Golgi apparatus) Cisternae trans face (“shipping” side of TEM of Golgi apparatus Golgi apparatus) Figure 6.12a 0.1 m TEM of Golgi apparatus Lysosomes: Digestive Compartments A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids Lysosomal enzymes work best in the acidic environment inside the lysosome © 2011 Pearson Education, Inc.  Animation: Lysosome Formation Right-click slide / select “Play” © 2011 Pearson Education, Inc.  Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole A lysosome fuses with the food vacuole and digests the molecules Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy © 2011 Pearson Education, Inc. Figure 6.13 1 m Vesicle containing Nucleus two damaged 1 m organelles Mitochondrion fragment Lysosome Peroxisome fragment Digestive enzymes Lysosome Lysosome Plasma membrane Peroxisome Digestion Food vacuole Mitochondrion Digestion Vesicle (a) Phagocytosis (b) Autophagy Figure 6.13a 1 m Nucleus Lysosome Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole (a) Phagocytosis Figure 6.13aa 1 m Nucleus Lysosome Figure 6.13b Vesicle containing two damaged 1 m organelles Mitochondrion fragment Peroxisome fragment Lysosome Peroxisome Mitochondrion Digestion Vesicle (b) Autophagy Figure 6.13bb Vesicle containing two damaged 1 m organelles Mitochondrion fragment Peroxisome fragment Vacuoles: Diverse Maintenance Compartments A plant cell or fungal cell may have one or several vacuoles, derived from endoplasmic reticulum and Golgi apparatus © 2011 Pearson Education, Inc.  Food vacuoles are formed by phagocytosis Contractile vacuoles, found in many freshwater protists, pump excess water out of cells Central vacuoles, found in many mature plant cells, hold organic compounds and water © 2011 Pearson Education, Inc.  Video: Paramecium Vacuole © 2011 Pearson Education, Inc. Figure 6.14 Central vacuole Cytosol Central Nucleus vacuole Cell wall Chloroplast 5 m Figure 6.14a Cytosol Central Nucleus vacuole Cell wall Chloroplast 5 m The Endomembrane System: A Review The endomembrane system is a complex and dynamic player in the cell’s compartmental organization © 2011 Pearson Education, Inc. Figure 6.15-1 Nucleus Rough ER Smooth ER Plasma membrane Figure 6.15-2 Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi Figure 6.15-3 Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi Concept 6.5: Mitochondria and chloroplasts change energy from one form to another Mitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP Chloroplasts, found in plants and algae, are the sites of photosynthesis Peroxisomes are oxidative organelles © 2011 Pearson Education, Inc. The Evolutionary Origins of Mitochondria and Chloroplasts Mitochondria and chloroplasts have similarities with bacteria – Enveloped by a double membrane – Contain free ribosomes and circular DNA molecules – Grow and reproduce somewhat independently in cells © 2011 Pearson Education, Inc.  The Endosymbiont theory – An early ancestor of eukaryotic cells engulfed a nonphotosynthetic prokaryotic cell, which formed an endosymbiont relationship with its host – The host cell and endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion – At least one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts © 2011 Pearson Education, Inc. Figure 6.16 Endoplasmic Nucleus reticulum Engulfing of oxygen- Nuclear using nonphotosynthetic envelope prokaryote, which becomes a mitochondrion Mitochondrion Ancestor of eukaryotic cells (host cell) Engulfing of photosynthetic prokaryote At least Nonphotosynthetic one cell Chloroplast eukaryote Mitochondrion Photosynthetic eukaryote Mitochondria: Chemical Energy Conversion Mitochondria are in nearly all eukaryotic cells They have a smooth outer membrane and an inner membrane folded into cristae The inner membrane creates two compartments: intermembrane space and mitochondrial matrix Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix Cristae present a large surface area for enzymes that synthesize ATP © 2011 Pearson Education, Inc. Figure 6.17 10 m Intermembrane space Outer Mitochondria membrane DNA Inner Free Mitochondrial membrane ribosomes DNA in the Cristae mitochondrial Nuclear DNA Matrix matrix 0.1 m (a) Diagram and TEM of mitochondrion (b) Network of mitochondria in a protist cell (LM) Figure 6.17a Intermembrane space Outer membrane DNA Inner Free membrane ribosomes in the Cristae mitochondrial Matrix matrix 0.1 m (a) Diagram and TEM of mitochondrion Figure 6.17aa Outer membrane Inner membrane Cristae Matrix 0.1 m Figure 6.17b 10 m Mitochondria Mitochondrial DNA Nuclear DNA (b) Network of mitochondria in a protist cell (LM) Chloroplasts: Capture of Light Energy Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis Chloroplasts are found in leaves and other green organs of plants and in algae © 2011 Pearson Education, Inc.  Chloroplast structure includes – Thylakoids, membranous sacs, stacked to form a granum – Stroma, the internal fluid The chloroplast is one of a group of plant organelles, called plastids © 2011 Pearson Education, Inc. Figure 6.18 Ribosomes 50 m Stroma Inner and outer membranes Granum Chloroplasts (red) DNA Thylakoid Intermembrane space 1 m (a) Diagram and TEM of chloroplast (b) Chloroplasts in an algal cell Figure 6.18a Ribosomes Stroma Inner and outer membranes Granum DNA Thylakoid Intermembrane space 1 m (a) Diagram and TEM of chloroplast Figure 6.18aa Stroma Inner and outer membranes Granum 1 m Figure 6.18b 50 m Chloroplasts (red) (b) Chloroplasts in an algal cell Peroxisomes: Oxidation Peroxisomes are specialized metabolic compartments bounded by a single membrane Peroxisomes produce hydrogen peroxide and convert it to water Peroxisomes perform reactions with many different functions How peroxisomes are related to other organelles is still unknown © 2011 Pearson Education, Inc. Figure 6.19 1 m Chloroplast Peroxisome Mitochondrion Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell The cytoskeleton is a network of fibers extending throughout the cytoplasm It organizes the cell’s structures and activities, anchoring many organelles It is composed of three types of molecular structures – Microtubules – Microfilaments – Intermediate filaments © 2011 Pearson Education, Inc. Figure 6.20 10 m Roles of the Cytoskeleton: Support and Motility The cytoskeleton helps to support the cell and maintain its shape It interacts with motor proteins to produce motility Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton Recent evidence suggests that the cytoskeleton may help regulate biochemical activities © 2011 Pearson Education, Inc. Figure 6.21 Vesicle ATP Receptor for motor protein Motor protein Microtubule (ATP powered) of cytoskeleton (a) Microtubule Vesicles 0.25 m (b) Figure 6.21a Microtubule Vesicles 0.25 m (b) Components of the Cytoskeleton Three main types of fibers make up the cytoskeleton – Microtubules are the thickest of the three components of the cytoskeleton – Microfilaments, also called actin filaments, are the thinnest components – Intermediate filaments are fibers with diameters in a middle range © 2011 Pearson Education, Inc. Table 6.1 10 m 10 m 5 m Column of tubulin dimers Keratin proteins Actin subunit Fibrous subunit (keratins 25 nm coiled together) 7 nm 8− 12 nm   Tubulin dimer Table 6.1a 10 m Column of tubulin dimers 25 nm   Tubulin dimer Table 6.1aa 10 m Table 6.1b 10 m Actin subunit 7 nm Table 6.1bb 10 m Table 6.1c 5 m Keratin proteins Fibrous subunit (keratins coiled together) 8−12 nm Table 6.1cc 5 m Microtubules Microtubules are hollow rods about 25 nm in diameter and about 200 nm to 25 microns long Functions of microtubules – Shaping the cell – Guiding movement of organelles – Separating chromosomes during cell division © 2011 Pearson Education, Inc.  Centrosomes and Centrioles In many cells, microtubules grow out from a centrosome near the nucleus The centrosome is a “microtubule-organizing center” In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring © 2011 Pearson Education, Inc. Figure 6.22 Centrosome Microtubule Centrioles 0.25 m Longitudinal section of one centriole Microtubules Cross section of the other centriole Figure 6.22a 0.25 m Longitudinal section of one centriole Microtubules Cross section of the other centriole  Cilia and Flagella Microtubules control the beating of cilia and flagella, locomotor appendages of some cells Cilia and flagella differ in their beating patterns © 2011 Pearson Education, Inc.  Video: Chlamydomonas © 2011 Pearson Education, Inc.  Video: Paramecium Cilia © 2011 Pearson Education, Inc. Figure 6.23 Direction of swimming (a) Motion of flagella 5 m Direction of organism’s movement Power stroke Recovery stroke (b) Motion of cilia 15 m Figure 6.23a 5 m Figure 6.23b 15 m  Cilia and flagella share a common structure – A core of microtubules sheathed by the plasma membrane – A basal body that anchors the cilium or flagellum – A motor protein called dynein, which drives the bending movements of a cilium or flagellum © 2011 Pearson Education, Inc.  Animation: Cilia and Flagella Right-click slide / select “Play” © 2011 Pearson Education, Inc. Figure 6.24 0.1  m Outer microtubule Plasma membrane doublet Dynein proteins Central microtubule Radial spoke Microtubules Cross-linking proteins between outer doublets (b) Cross section of Plasma motile cilium membrane Basal body 0.5  m 0.1  m (a) Longitudinal section Triplet of motile cilium (c) Cross section of basal body Figure 6.24a Microtubules Plasma membrane Basal body 0.5 m (a) Longitudinal section of motile cilium Figure 6.24b 0.1 m Outer microtubule Plasma membrane doublet Dynein proteins Central microtubule Radial spoke Cross-linking proteins between outer doublets (b) Cross section of motile cilium Figure 6.24ba 0.1 m Outer microtubule doublet Dynein proteins Central microtubule Radial spoke Cross-linking proteins between outer doublets (b) Cross section of motile cilium Figure 6.24c 0.1 m Triplet (c) Cross section of basal body Figure 6.24ca 0.1 m Triplet (c) Cross section of basal body  How dynein “walking” moves flagella and cilia − Dynein arms alternately grab, move, and release the outer microtubules – Protein cross-links limit sliding – Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum © 2011 Pearson Education, Inc. Figure 6.25 Microtubule ATP doublets Dynein protein (a) Effect of unrestrained dynein movement Cross-linking proteins ATP between outer doublets Anchorage in cell (b) Effect of cross-linking proteins 1 3 2 (c) Wavelike motion Figure 6.25a Microtubule doublets ATP Dynein protein (a) Effect of unrestrained dynein movement Figure 6.25b Cross-linking proteins ATP between outer doublets 1 3 2 Anchorage in cell (b) Effect of cross-linking proteins (c) Wavelike motion Microfilaments (Actin Filaments) Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits The structural role of microfilaments is to bear tension, resisting pulling forces within the cell They form a 3-D network called the cortex just inside the plasma membrane to help support the cell’s shape Bundles of microfilaments make up the core of microvilli of intestinal cells © 2011 Pearson Education, Inc. Figure 6.26 Microvillus Plasma membrane Microfilaments (actin filaments) Intermediate filaments 0.25 m  Microfilaments that function in cellular motility contain the protein myosin in addition to actin In muscle cells, thousands of actin filaments are arranged parallel to one another Thicker filaments composed of myosin interdigitate with the thinner actin fibers © 2011 Pearson Education, Inc. Figure 6.27 Muscle cell 0.5 m Actin filament Myosin filament Myosin head (a) Myosin motors in muscle cell contraction Cortex (outer cytoplasm): gel with actin network 100 m Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Chloroplast 30 m (c) Cytoplasmic streaming in plant cells Figure 6.27a Muscle cell 0.5 m Actin filament Myosin filament Myosin head (a) Myosin motors in muscle cell contraction Figure 6.27aa 0.5 m Figure 6.27b Cortex (outer cytoplasm): gel with actin network 100 m Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement Figure 6.27c Chloroplast 30 m (c) Cytoplasmic streaming in plant cells  Localized contraction brought about by actin and myosin also drives amoeboid movement Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments © 2011 Pearson Education, Inc.  Cytoplasmic streaming is a circular flow of cytoplasm within cells This streaming speeds distribution of materials within the cell In plant cells, actin-myosin interactions and sol- gel transformations drive cytoplasmic streaming © 2011 Pearson Education, Inc.  Video: Cytoplasmic Streaming © 2011 Pearson Education, Inc. Intermediate Filaments Intermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubules They support cell shape and fix organelles in place Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes © 2011 Pearson Education, Inc. Concept 6.7: Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials that are external to the plasma membrane These extracellular structures include – Cell walls of plants – The extracellular matrix (ECM) of animal cells – Intercellular junctions © 2011 Pearson Education, Inc. Cell Walls of Plants The cell wall is an extracellular structure that distinguishes plant cells from animal cells Prokaryotes, fungi, and some protists also have cell walls The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein © 2011 Pearson Education, Inc.  Plant cell walls may have multiple layers – Primary cell wall: relatively thin and flexible – Middle lamella: thin layer between primary walls of adjacent cells – Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall Plasmodesmata are channels between adjacent plant cells © 2011 Pearson Education, Inc. Figure 6.28 Secondary cell wall Primary cell wall Middle lamella 1 m Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata Figure 6.28a Secondary cell wall Primary cell wall Middle lamella 1 m Figure 6.29 RESULTS 10 m Distribution of cellulose Distribution of synthase over time microtubules over time Figure 6.29a 10 m Distribution of cellulose synthase over time Figure 6.29b 10 m Distribution of microtubules over time  The Extracellular Matrix (ECM) of Animal Cells Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin ECM proteins bind to receptor proteins in the plasma membrane called integrins © 2011 Pearson Education, Inc. Figure 6.30 Collagen EXTRACELLULAR FLUID Polysaccharide molecule Proteoglycan Carbo- complex hydrates Fibronectin Core protein Integrins Proteoglycan molecule Plasma membrane Proteoglycan complex Micro- CYTOPLASM filaments Figure 6.30a Collagen EXTRACELLULAR FLUID Proteoglycan complex Fibronectin Integrins Plasma membrane CYTOPLASM Micro- filaments Figure 6.30b Polysaccharide molecule Carbohydrates Core protein Proteoglycan molecule Proteoglycan complex  Functions of the ECM – Support – Adhesion – Movement – Regulation © 2011 Pearson Education, Inc. Cell Junctions Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact Intercellular junctions facilitate this contact There are several types of intercellular junctions – Plasmodesmata – Tight junctions – Desmosomes – Gap junctions © 2011 Pearson Education, Inc. Plasmodesmata in Plant Cells Plasmodesmata are channels that perforate plant cell walls Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell © 2011 Pearson Education, Inc. Figure 6.31 Cell walls Interior of cell Interior of cell 0.5 m Plasmodesmata Plasma membranes  Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid Desmosomes (anchoring junctions) fasten cells together into strong sheets Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells © 2011 Pearson Education, Inc.  Animation: Tight Junctions Right-click slide / select “Play” © 2011 Pearson Education, Inc.  Animation: Desmosomes Right-click slide / select “Play” © 2011 Pearson Education, Inc.  Animation: Gap Junctions Right-click slide / select “Play” © 2011 Pearson Education, Inc. Figure 6.32 Tight junctions prevent fluid from moving Tight junction across a layer of cells TEM 0.5 m Tight junction Intermediate filaments Desmosome TEM 1 m Gap junction Ions or small molecules Space TEM between cells Extracellular Plasma membranes matrix of adjacent cells 0.1 m Figure 6.32a Tight junctions prevent fluid from moving across a layer of cells Tight junction Intermediate filaments Desmosome Gap junction Ions or small Plasma membranes molecules of adjacent cells Space between cells Extracellular matrix Figure 6.32b Tight junction TEM 0.5 m Figure 6.32c TEM 1 m Figure 6.32d TEM 0.1 m The Cell: A Living Unit Greater Than the Sum of Its Parts Cells rely on the integration of structures and organelles in order to function For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane © 2011 Pearson Education, Inc. Figure 6.33 5 m Figure 6.UN01 Nucleus (ER) (Nuclear envelope) Figure 6.UN01a Nucleus (ER) Figure 6.UN01b (Nuclear envelope) Figure 6.UN01c Figure 6.UN02 Figure 6.UN03 Figure 6.UN04